Sleepers, ‘Q cars’, call them what you will, my heart has ached over cars like the Audi RS6 since childhood. My towering brochure collection is testament to this. There’s something extra special about cars that look relatively ordinary but can give supercars a run for their money and probably even embarrass them. A person who’s really not that into cars could be forgiven for mistaking the RS6 for a common or garden S-Line Audi estate. The fact that it can hit 62mph in under four seconds results in many an open mouth. If you’re a Labrador and your owner buys one, brace yourself; and it’d probably be wise to take a sick bag, too.

Look more closely at the RS6 and you’ll notice the swollen wheel arches, even more dominant honeycomb grille, flared nostrils, gaping oval exhausts, splitter and diffuser. This, the C7 generation RS6, is only sold in Avant estate guise, which is no doubt a clever marketing ploy by Audi. The £4,450 Carbon Styling Package makes this relatively covert vehicle look even more aesthetically alluring, but having the grille adorned with hefty quattro lettering may not be to everyone’s taste. I wasn’t sure about the Daytona grey pearl paint job at first, but by the end of the week, it’d grown on me considerably. After all, I’m a fairly shy bloke. I must admit iconic Sepang Blue would look great on the 2015 RS6, too, though.

In my reckoning, Audi currently leads the way when it comes to interiors. Not a single whiff of cheesiness is present, not even the pop-out multimedia screen which, yes, may break after a decade or so. In darker shades, like my test RS6’s black, they may be slightly sombre, but Audi interiors are impeccably constructed, exude quality and on the whole feel like they will last forever. If I was fortunate enough to be able to order my own RS6, I’d specify it with quilted Lunar Silver Valcona honeycomb leather. The diamond-stitched Alcantara and leather in the test car would be easier to clean, though, if one had an embarrassing trouser mishap during break-neck cornering. It’d be more suitable, too, for people heroic enough to use their RS6 for trips to the council tip or nearest Swedish furniture retailer.

This car really is Jack of all trades, master of many, with the ability to look en vogue whether it’s parked outside the office, at the beach or tearing around a racing circuit. One friend aptly described the grey RS6 as a cage fighter in a pinstripe suit. It’s barking mad and I absolutely love it. The rate of acceleration from this road-going Messerschmitt can feel frightening at times, living up to its incredible ‘on paper’ statistics. Permanent Quattro and a self-locking centre differential certainly help the 560bhp RS6 lay down its brutish 700Nm torque, and the 8-speed tiptronic transmission does it ever so smoothly. If a top speed of 155mph seems a bit feeble, you can open up 189mph courtesy of the Dynamic Package Plus, which costs £11,500. The RS6 stops impressively, too, thanks to 275/35 tyres and hefty brakes.

Mercedes’ E63 AMG Estate produces around the same torque but the Audi is faster than the BMW M5 and Jaguar XFR-S Sportbrake. If, like me, you get kicks from a snap, crackle and pop V8 soundtrack, you may be a little disappointed with the 2015 RS6’s stock exhaust. It’s relatively subdued much of the time, as Audi’s clever Cylinder on Demand technology allows the 4-litre V8 engine to run on four cylinders when possible. There is a £1,000 Sports Exhaust upgrade, but if you’re clever with the flappy paddles, you can still conduct an orchestra of splendid sounds.

Nobody who experienced the RS6 could believe how bizarrely smooth, comfortable, composed and refined the ride quality felt, even in Dynamic mode. Granted, air suspension often results in such characteristics, but with such colossal alloys shod with low profile rubber, it was a pleasant surprise. Cars engineered for handling agility tend to come with bone-jarring rides, making them less lovable for everyday use – but not this one.

In the back, there’s oodles of space for a couple of large adults, but the pronounced transmission tunnel means the middle seat is best used by a child. With 565/1,680 litres on offer, the RS6’s boot is less accommodating than the Mercedes E63 AMG Estate, which avails 695/1,950 litres. The Audi’s boot comes with many practical storage features, though, and folding the back seats flat is a doddle thanks to the quick release system.

No car is perfect, however, and in the RS6’s case, the slight let-down is that its electromechanical steering falls a little short in terms of visceral engagement and communication. Steering feedback on challenging, snaking country roads isn’t quite upto M5 or XFR-S levels, which may leave some purists wanting for more. The Audi’s composure, tremendous grip and breath-taking speed compensate nicely in my view, though, making it a super estate for all weathers.

A menacing beast like this is always going to err on the thirsty side. On paper, the RS6 will return upto 28.8mpg and after 600 miles or so of largely quite aggressive driving, we averaged just over 20mpg. This makes the Audi marginally thirstier than its rivals, but it’s worth bearing in mind that although the BMW M5 saloon and Mercedes-Benz E63 AMG Estate cost around the same as the RS6, the Jaguar XFR-S Sportbrake is the most expensive of the bunch.

When some childhood dreams materialise, it can be anticlimactic. Not in the RS6’s case, though, albeit now the C7 generation. The relatively muted exhaust issue can easily be resolved, its face-warping acceleration made up for any comparable lack in steering feedback, and unless you’ll be venturing onto the track or autobahn, 155mph is more than enough. A car like this is naturally going to require deep pockets to buy and run, but for those in the nice position to be able to contemplate one, the Audi RS6 is, in my view, the best all-rounder. It’s an epic car.